1. Field of the Invention
This invention relates to electrolytic cell monitoring for electrometallurgical systems, including, for example, i) electrorefining and electrowinning systems for copper, zinc, nickel, lead, cobalt, and other like metals, ii) electrochemical cells, such as chlor-alkali systems, and iii) molten salt electrolysis, such as aluminum and magnesium electrolysis.
Insofar as the inventive arrangements can be used with electrolytic cell monitoring during a copper refinement stage of producing copper, copper production will be described hereinout for exemplary, representative, and non-limiting purposes.
2. Description of Related Art
Producing copper involves a series of steps involving mining, crushing and grinding, concentrating, smelting, converting, and refining procedures, each of which is well-known, shown in block diagram format in FIG. 1, and elaborated upon below. As depicted, mining 10 loosens and collects ore. Crushing and grinding 12 turn the ore into a crushed and ground ore, comprising a fine powder in which desired ore minerals are liberated. Concentration 14 collects the desired ore minerals into a watery slurry, which is then filtered and dried to produce a liquid concentrate suitable for smelting. Smelting 16 smelts (i.e., melts and oxidizes) iron and sulfur in the liquid concentrate to produce a copper matte. Conversion 18 converts the copper matte by oxidation into a blister copper. And finally, refinement 20 refines the blister copper into a more refined copper.
Referring now to FIG. 1, more specific descriptions will now be provided for further exemplary, representative, and non-limiting purposes:
A. Mining 10
As known, large amounts of ore containing various minerals exist beneath the surface of the Earth, comprising one or more of a copper sulfide or copper-iron-sulfide mineral, such as chalcocite, chalcopyrite, and bornite. Holes are drilled into this ore so that explosives can be detonated to loosen the ore and make it amenable to loading and hauling to a crushing and grinding facility.
B. Crushing and Grinding 12
At the crushing and grinding facility, the ore is crushed, mixed with water, and ground into a fine powder by various ore crushing and grinding mechanisms, after which it is pumped to a concentration facility. Crushed and ground ore typically contains less than 2 weight percent (“wt %”) copper.
C. Concentration 14
At the concentration facility, the crushed and ground ore is concentrated into a slurry liquid concentrate. More specifically, the crushed and ground ore is mixed with water, chemicals, and air in a floatation cell, which causes copper in the crushed and ground ore to stick to air bubbles rising within the flotation cell. As the air bubbles float to the top of the surface of the flotation cell, they are collected to form the liquid concentrate.
Thus, concentration 14 concentrates the crushed and ground ore into slurry liquid concentrate, which typically contains approximately 25-35 wt % copper (and 20-30 wt % water). Using various filters, the concentrate is then dewatered to produce a moist copper concentrate that is amenable to handling by conveyor belts, loaders, rail cars, and the like.
D. Smelting 16
Using heat and oxygen, the concentrate is smelted into a slag and copper-iron sulfide called copper matte. More specifically, the moist concentrate is first dried in a large, rotating drum or similar drying apparatus. Then, it is fed into a smelting process in which the now-dried concentrate is mixed with oxygen-enriched air and blown into a smelting furnace through a concentrate burner. Within the smelting furnace, the now-dried concentrate is exposed to temperatures greater than 2300° Fahrenheit, by which it partially oxidizes and melts due to heat generated by oxidizing sulfur and iron within the molten concentrate.
This process generates the following three products: i) off-gases, ii) slag, and iii) copper matte. The off-gases, which include sulfur dioxide (i.e., SO2), are routed to a waste gas handling system through an off-take riser in the smelting furnace. The slag comprises silica and iron, or more specifically, gangue mineral, flux, and iron oxides, and it has a low specific gravity (i.e., lower density) relative to the copper matte, thus allowing it to float on top of the copper matte. The copper matte, on the other hand, comprises copper sulfide and iron sulfide, and it has a high specific gravity (i.e., higher density) relative to the slag, thus allowing it to form, collect, and sink to a basin or settler located at the bottom of the smelting furnace.
Periodically, the slag is tapped off. More specifically, the slag and copper matte are conventionally separated by skimming the slag from the copper matte through various tap-holes in sidewalls of the smelting furnace. These tap-holes are commonly located at a relatively high elevation on the sidewalls to allow the slag to be removed from the smelting furnace without removing the copper matte. Conversely, various tap-holes for the copper matte are commonly located at a relatively low elevation on the sidewalls to allow the copper matte to be removed from the smelting furnace without removing the slag.
Thus, smelting 16 smelts the liquid concentrate into copper matte, which typically contains approximately 35-75 wt % copper.
E. Conversion 18
After the slag is separated from the copper matte, the copper matte can be i) transferred directly into a conversion furnace, ii) transferred into a holding furnace for subsequent delivery to the conversion furnace, or iii) converted into a solid form by flash-cooling the copper matte in water to form granules, which are stock-piled in a large, enclosed space for subsequent delivery to the conversion furnace. Within the conversion furnace, various remaining impurities are removed from the copper matte, and the result produces a molten copper called blister copper.
There are two basic types of conversion furnaces—namely, flash conversion furnaces and bath conversion furnaces. The purpose of each is to oxidize (i.e., convert) metal sulfides to metal oxides. Representative flash conversion furnaces, which are also known as suspension furnaces, include the flash conversion furnace used by Kennecott Utah Copper Corp. at its Magna, Utah facility. Representative bath conversion furnaces include the bath conversion furnaces used by i) Noranda, Inc. at its Horne, Canada facility; ii) Inco Ltd. at its Sudbury, Canada facility; and iii) Mitsubishi Materials Corp. at its Naoshima, Japan facility.
Regardless of the type of conversion furnace, the copper matte is converted into blister copper within the conversion furnace by the reaction of the copper matte with oxygen. More specifically, in bath conversion furnaces, the molten copper matte is charged into the furnace and air or oxygen-enriched air is blown into the molten copper matte through tuyeres or gas injectors. Silica flux is added to the bath conversion furnace to combine with the iron being oxidized and form the slag.
Flash conversion processes, on the other hand, treat solidified copper matte by first grinding the matte to a suitable size (i.e., a powder) and then blowing this into a flash reaction furnace using oxygen enriched air (ca. 70-90% oxygen). Flux is also added to the powdered matte, typically as calcium oxide, but it may also be silica or a combination of calcium oxide and silica. The powdered matte combusts in the oxygen atmosphere and generates sufficient heat to melt the materials and flux and produce molten blister and slag.
These conversion processes generate the following two products: i) slag and ii) blister copper. The slag comprises gangue mineral, copper metal (i.e., Cu0), copper oxides (principally in the form of Cu2O), flux, and iron oxides, and it has a low specific gravity (i.e., lower density) relative to the blister copper, thus allowing it to float on top of the blister copper. The blister copper, on the other hand, comprises gangue mineral, copper metal (i.e., Cu0), copper oxides (principally in the form of Cu2O), and copper sulfides (principally in the form of Cu2S), and it has a high specific gravity (i.e., higher density) relative to the slag, thus allowing it to form, collect, and sink to a basin or settler located at the bottom of the conversion furnace. While the top slag layer is typically approximately thirty centimeters deep, the bottom blister copper layer is approximately fifty centimeters deep.
If the conversion furnace is a rotary bath conversion furnace, then the slag and blister copper are separately poured from a mouth or spout on an intermittent basis. If, on the other hand, the conversion furnace is stationary bath conversion furnace, then outlets are provided for removing the slag and blister copper. These outlets typically include various tap-holes that are located at varying elevations on one or more sidewalls of the conversion furnace, and, in a manner similar to that used with the smelting furnace, each is removed from the conversion furnace independently of the other. Other types of conversion furnaces commonly utilize one or more outlets to continuously overflow the slag and blister copper, using, for example, an appropriate weir to retain the slag.
The phase separation that occurs between the slag and blister copper is not complete. Thus, the slag, as indicated, contains additional copper, which is usually in the form of copper metal (i.e., Cu0) and copper oxides (principally in the form of Cu2O), while the blister copper contains various waste and un-recovered minerals (e.g., sulfur), which are principally in the form of copper oxides (principally in the form of Cu2O), copper sulfides (principally in the form of Cu2S), and ferrosilicates, etc. The copper that is in the slag has a lost metal value, which can be recovered by recycling the slag back to the smelting furnace, while the waste and un-recovered mineral values in the blister copper constitute impurities that are eventually removed in either an anode furnace or through electrorefining.
Thus, conversion 18 converts the copper matte into blister copper, which typically contains more than 98 wt % copper.
F. Refinement 20
Finally, the blister copper is refined, usually first pyrometallurgically and then electrolytically. More specifically, the blister copper is subjected to an additional purification step to further up-grade the copper content, such as fire refining in a reverberatory or rotary anode furnace. Then, the blister copper is cast into large, thick plates called anodes, which are often transferred from an anode casting plant to the electrolytic copper refinery by truck, rail, or the like. In the electrolytic copper refinery, the anodes are lowered into an acidic solution that contains approximately 120-250 gpl of free sulfuric acid and approximately 30-50 gpl of dissolved copper. Then the anodes are electrically connected to a positive direct current supply. To electrolyze the anodes in this aqueous electrolyte, they are separated by insoluble, interleaved stainless steel blanks called starter sheets or cathodes, which are negatively charged. Electricity is then sent between the anodes and cathodes for a pre-determined length of time, causing copper ions to migrate from the anodes to the cathodes to form plates at the cathodes, which contain less than 20 parts per million impurities (i.e., sulfur plus non-copper metals, but not including oxygen). Voltages of approximately 0.1-0.5 volts are generally sufficient to dissolve the anodes and deposit the copper on the cathodes, with corresponding current densities of approximately 160-380 amps/m2. With each anode producing two cathode plates at which the refined copper is deposited, the cathodes are then washed and ready for an ultimate end use.
In a typical copper refinery producing 300,000 tons of copper cathode per year, there can be as many as 1,440 electrolytic cells, each with 46 anodes and 45 cathode blanks, for a total of 131,000 pieces suspended into the cells. In such a traditional copper refinery, each cathode and each anode is electrically connected to the refinery current supply system through two or more contact points on the supporting ears of the anodes and the hanger bars of the cathodes. This means there can be a total of over 260,000 electrical connections (i.e., two per anode and two per cathode multiplied by the number of cathodes and anodes). Critical to the efficient operation of the refining process is the absence of short circuits between the anodes and cathode blanks. As subsequently elaborated upon, short circuits can occur if the anodes and cathodes are mis-aligned or if copper deposits on the cathode grow in a non uniform manner and contact the anode. When short circuits do occur, the desired copper plating process is disrupted and the efficiency of electrical use decreases. Accordingly, the short circuits result in decreasing the voltage differential across the anodes and cathodes.
Critical to the efficient operation of the refining process is the absence of open and short circuits between the anodes and cathodes. As subsequently elaborated upon, short circuits can occur if the anodes and cathodes are mis-aligned or if copper deposits on the cathode grow in a non-uniform manner and contact the anode. When short circuits do occur, the desired copper plating process is disrupted. Open circuits, on the other hand, can occur if there is poor contact between the current supply and the anodes or cathodes. When open circuits do occur, the efficiency of electrical use decreases.
Thus, refinement 20 refines the blister copper into refined copper, which typically contains approximately 99.99 wt % copper (i.e., effectively, pure copper).
Thereafter, refinement 20 allows the refined cathode copper to be converted into any number of copper end-products using conventional methods and techniques, which are well-known in the art.
The efficiency of copper refinement 20 can be increased by increasing the efficiency of cell monitoring. More specifically, at least one important cell parameter needs to be closely monitored—namely, electrical current flow through each individual cathode in the electrolytic cell. Failure to adequately monitor this cell parameter, and others, can reduce metal recovery, increase scrap rate, and lead to inefficient energy utilization. Nevertheless, open and short circuits commonly occur during the electrolytic refining of copper. They occur for many reasons, including i) poor anode and cathode physical qualities, ii) poor contact between the current supply and the anodes or cathodes, iii) misalignment of anodes and cathodes, and iv) localized variations in electrolyte temperature, additive levels, or chemistry. Thus, efficient electrolytic cell monitoring is important during the electrolytic refining of copper, as it can enable system operators to detect open and short circuits between anodes and cathodes, which, if not corrected, reduce current efficiencies and result in down-stream processing problems, such as poor cathode development. As known, copper impurity, copper content, and copper appearance are also ultimately adversely affected by open and short circuits.
Conventional monitoring focused on only identifying short circuits between the anodes and cathodes. This was commonly accomplished by manually using a hand-held Gauss meter to detect abnormal magnetic fields flowing through the cathode. Such a procedure generally required physically walking over the anodes and cathodes in each cell while closely observing the hand-held Gauss meter to detect a large deflection in a meter needle. Oftentimes, the Gauss meter was affixed to a distal end of a long stick or pole, whereby it can then be held close to the cathode hanger bar. Regardless, the task was both ergonomically difficult and accident-prone. Moreover, walking on the cells frequently misaligned the anode and cathodes, could lead to possible contamination, and often lead to further problems as well.
Since shorts generate heat, newly-developed techniques have involved using infrared cameras and image processing techniques. However, like the traditional Gauss meter techniques, these generally only detect short circuits and not open circuits.
While detecting open and short circuits deals with their effects rather than their causes, it is a widely recognized technique for improving electrode quality. Accordingly, after a short circuit is detected, it is generally cleared by probing between the anode and cathode with a stainless steel rod to locate the fault and then physically separating (i.e., breaking off) an errant copper nodule growing at the epicenter of the short circuit. This often requires physically lifting the cathode out of the cell. Unfortunately, however, many open and short circuits are not often detected until after significant damage has already occurred.
Consequently, there is a need for an improved electrolytic cell current monitoring device and method, which detect not only short circuits, but open circuits as well. Such a device and method will increase energy utilization and efficiency during the copper refinement stage 20 of producing copper. Thus, a need exists for effective monitoring electrolytic cell currents during the copper refinement stage 20 of producing copper.